1. Field of the Invention
This invention relates to a sweep generator for a seismic source vibrator and more particularly to a sweep generator capable of generating desired sweep signals determined by input parameters.
2. Description of the Prior Art
Linear frequency envelopes for geophysical prospecting having been commonly used in the past and are presently being used.
In recent years there has been interest in the use of non-linear frequency envelopes such as logarithmic and quadratic. In the prior art, to generate the sweep signal at each vibrator, each vibrator control unit is equipped with various firmware subroutines for digital generation of each of the defined sweep modes. In most of those prior art systems, the various sweep modes are accessed via manual switches located on each vibrator control unit. The systems require large memories for storing all of the points necessary to define each desired sweep.
This invention provides for generating any desired sweep signal without changing firmware by providing in memory an interpolation equation for the computation of instantaneous frequency or amplitude values. To effect the change in the sweep mode to be used, a change in the input parameters is required.